The present invention relates generally to endoluminal prostheses, and more specifically to an endoluminal prosthesis comprising a stent with an overlying graft cover, and a delivery system and method for delivering and deploying the prosthesis.
As an alternative to traditional surgical vascular treatments where tissues are cut to reach a damaged artery or vein, xe2x80x9cendovascularxe2x80x9d treatments are now frequently used. Endovascular and related treatments are carried out at the lumen of the vessel. Some exemplary purposes and means for such treatments may be:
a) to produce artery or vein dilatation,
b) to dissolve thrombus in their interior,
c) to close abnormal communications of vessels among each other or with neighboring tissues,
d) to carpet the surface of a vessel with a prosthesis, as a xe2x80x9csheathingxe2x80x9d,
e) to return a dilated artery (aneurysm) to its normal caliber, or
f) to isolate the inner surface of an artery from the blood chemical or physical elements, such as, for example, after performing dilatation with a balloon (internal bypass).
Endovascular expanders, commonly known as xe2x80x9cstentsxe2x80x9d, are often used to carry out the above techniques. Stents are generally tubular, permeable, elastic structures that are typically structured in special metallic meshes forming skeletal expandable tubes able to generate radial forces to keep vessels open.
Essentially, there are three general types of stents: thermosensitive self-expanding stents, which adopt predetermined shapes at different temperatures, particularly that of the human body (such as, for example, as described in U.S. Pat. No. 4,425,908); stents expandable with a balloon (such as, for example, as described in European Patent EP 378151), and stents that are self-expandable through structural elasticity (such as, for example, as described in U.S. Pat. No. 4,580,568 to Cesare Gianturco).
Self-expandable stents are typically compressed inside introductory devices or sheaths. Once the vascular area is reached, the sheath is removed, allowing the stent to expand into an endoluminal deployment location. Commonly used stents of this type are described in patents to Cesare Gianturco or in patents assigned to Schneider (USA) Inc. of Plymouth, Minn. or Schneider (Europe) A. G. of Bulach, Switzerland.
Because of their structure, self-expanding stents typically experience longitudinal lengthening when compressed inside the sheath. When liberated inside the vascular lumen, they radially expand and longitudinally reduce. This change in shape poses a serious problem when the stent is part of a prosthesis wherein the stent is covered or lined with a Dacron or a polytetraethylene graft outside of the stent.
When the stent is deployed and expansion occurs, the length of the graft remains essentially unchanged, while the stent noticeably shortens. For example, referring now to FIGS. 1 and 2, there are shown a compressed stent 12 and compressed graft 13 in FIG. 1 and an expanded stent 12xe2x80x2 and expanded graft 13xe2x80x2 in FIG. 2. FIGS. 1 and 2 illustrate the relatively substantial change in length of stent 12 upon expansion as compared to the insubstantial change in length of graft 13.
Thus, a graft that is the same length as the stent inside the sheath is too long when the stent is liberated. On the contrary, if the graft is too much shorter than the stent inside the sheath, parts of the stent remain without graft cover when the stent opens. Because of the different expansion properties between the graft and the stent, and the frictional relationship between the two in the sheath, irregular expansion of the graft may occur during deployment, provoking folds on the graft that act as constrictor rings to limit the expansion of the stent.
Thus there is a need in the art for a prosthesis, and a system and method for deployment thereof, that eliminates such problems associated with concurrent deployment of a stent and graft.
The present invention provides a prosthesis adapted for deployment inside a body lumen in a distal deployment location from a proximal access location outside the body lumen. The prosthesis comprises a graft having flexible walls and a distal end, and an expandable stent underlying the graft and having a proximal end and a distal end, the stent and graft being linked together only at or near the distal ends thereof. The stent and graft may each have a compressed radial configuration and an expanded radial configuration, each configuration having a corresponding axial length. The length of the stent in its compressed configuration exceeds the length of the stent in its expanded configuration by a difference in stent length. The length of the graft in its expanded configuration may be essentially equal to the graft in its compressed configuration, or may exceed the length of the graft in its compressed configuration by a difference in graft length. In either case, the difference in stent length exceeds the difference in graft length.
The present invention also includes an introducer adapted to endoluminally deploy such a prosthesis inside a body lumen in a distal deployment location from a proximal access location outside the body lumen, the introducer comprising an exterior sheath and an interior sheath axially mounted inside the exterior sheath. The graft is positioned between the interior and exterior sheaths and the stent is compressed at least partially inside the interior sheath.
The invention also includes a method for deploying an endoluminal prosthesis in accordance with this invention. The method comprises introducing the prosthesis into a deployment location in the body lumen using an introducer according to this invention, retracting the exterior sheath to liberate the graft therefrom, and then retracting the interior sheath to enable the stent to radially expand against the graft and bias the graft against the body lumen. The method may further comprise introducing the introducer into the deployment location with the introducer distal end located upstream relative to proximally flowing endoluminal fluid within the body lumen. During deployment of the stent, endoluminal fluid may flow between the graft and the inner sheath. In particular, the method may be used for deploying a prosthesis according to the present invention in a vascular lumen, wherein blood may flow between the graft and the inner sheath during deployment of the stent.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention.